An Adipose Mast-Cell Activation and Type-2 Orchestration Endotype of Lipedema: A Testable Neuroimmune Framework

Lipedema affects an estimated 11 to 12% of women and is characterized by bilateral, symmetric, painful enlargement of the limb subcutaneous fat that resists dietary weight loss. Its primary substrate is increasingly understood to be adipo-vascular and connective: genome-wide association studies implicate adipose, vascular, and extracellular-matrix loci rather than immune genes, and the affected fat is metabolically healthier than its mass predicts. Inflammation is itself well documented in lipedema tissue, but its type 2, reparative character suggests that it amplifies this substrate rather than initiating the disease. Against this substrate, however, a focused neuroimmune cluster remains unexplained by purely structural models: a diagnostically accurate quantitative sensory testing pattern, elevated tissue histamine, frequent comorbid fibromyalgia, and disease that is more severe in limbs carrying an additional local vascular trigger. We hypothesize that altered tissue mechanics and adipo-vascular biology help trigger a localized immune cascade, so that these observations may define a clinically identifiable subgroup exhibiting a type 2 immune and mast cell-activation endotype, nested within the broader adipo-vascular disorder. The core framework is deliberately limited to this testable sequence: adipo-vascular susceptibility, per-cell mast cell/type 2 activation, histaminergic peripheral sensitization, the quantitative sensory testing signature, and pain generation in a clinically identifiable endotype. We argue that the endotype is best characterized by per-cell mast cell secretory activity rather than abundance, which is not consistently increased in lipedema tissue. It is defined a priori, before treatment exposure, by a composite of baseline features (affected-fat erythema or warmth, atopic or mast cell-activation features, and the characteristic quantitative sensory testing pattern), with response to mast cell-directed therapy reserved as its prospective test rather than a defining criterion. We present the framework as a graded synthesis, distinguishing evidence shown directly in lipedema from that inferred from related fields and from untested hypotheses. Broader adipogenic, gut-immune, HLA-associated, cancer-related, ADHD-related, and systemic immunomodulatory concepts are separated into a dedicated exploratory section; they are secondary hypotheses and are not required for the central mast cell-histamine-QST-pain claim. The framework identifies mast cell activation as a potential therapeutic target in this subgroup for future investigation, pending prospective validation.